1. Field of the Invention
The present invention relates to defect inspection apparatus and a method of defect inspection detecting and inspecting defects of an inspected piece.
2. Description of the Related Art
Defect inspection apparatus has been used for the purpose of, for example, observing surface conditions of substrate having micro-structures represented by semiconductor devices formed thereon in an integrated manner, and confirming presence or absence of any defects.
The defect inspection apparatus is provided with a bright-field optical system having an illumination unit irradiating the inspected piece with an illumination beam, and taking an image of regular reflection beam from the inspected piece, or a dark-field optical system having an illumination unit irradiating the inspected piece with an illumination beam, and taking an image of irregular reflection beam from the inspected piece; and inspects defects on the surface of the inspected piece using either or both of the bright-field optical system and the dark-field optical system.
In recent years, a proposal has been made on a defect inspection apparatus capable of executing defect inspection and defect identification in an automated manner, as described in Patent Document 1 below, because visual defect inspection using a defect inspection apparatus casts a large operation load upon an operator and takes a long time for the operation.
Related art is disclosed in Japanese Patent No. 3415943.
In automatic judgment of presence or absence of the defects, the defect inspection apparatus preliminarily sets a predetermined threshold value with respect to intensity of the reflected beam from the inspected piece, and presence or absence of the defects is judged based on a magnitude relation between the threshold value and intensity of the reflected beam. Therefore, intensity of the reflected beam close to the threshold value inevitably destabilizes the judgment of presence or absence of the defects. Even if the threshold value is set in a stable region in which the reflected beam has only a small probability of showing intensity very close to the threshold value, judgment of presence or absence of the defects may be destabilized due to fluctuation in environment of the apparatus, such as set temperature in the apparatus, so that judgment of defects causing reflected beam having an intensity close to the threshold value is still more inevitably destabilized. Another problem resides in that quasi-defects, which do not exist on the real inspected piece, may be observed due to non-uniform color of the surface, and such quasi-defects often show an unstable behavior similarly due to fluctuations in environment of the apparatus.
There has never been proposed a technique of quantitatively understanding the defects (unstable defects) likely to destabilize the judgment of their existence, as being discriminated from the defects (stable defects) allowing stable judgment, so that the technique remains to be expected for further research and development for the future.